Tuesday, September 2, 2014

A new paper published in Chemical Geology finds the Iberian Peninsula was 'rather more humid' than today from 10,000-6,000 years ago including the Holocene Climate Optimum. The authors also find "Saharan dust [over Western Europe] is driven by solar forcing and 1.5–2.0 thousand year cycles," which affects regional climate due to dust aerosols in the atmosphere.

According to the paper

Effective humidity reconstruction indicates wetter conditions during the early Holocene and progressive aridification during middle–late Holocene time, boosting abrupt changes in the lacustrine system. Cyclostratigraphic analyses and transport mechanisms both point to solar irradianceand aridity as major triggering factors for dust supply over Western Europe during the Holocene.

Data from the paper shows the Iberian Peninsula was much more humid during the early-mid Holocene [past ~11,000 years] in good agreement with solar insolation, and per the Clausius–Clapeyron Relation, warmer air can hold more water vapor/humidity. The data shows humidity decreased to the lowest levels of the Holocene during the Little Ice Age and has recovered slightly since to the end of the record in 2006.

Thus, the data suggests the Sun drives humidity/aridity and dust transport, both of which have large effects upon climate and may add to many other solar amplification mechanisms described in the scientific literature.

Bottom graph shows the Iberian Peninsula was much more humid during the early-mid Holocene [past ~11,000 years] in good agreement with the solar insolation. The data shows humidity decreased to the lowest levels of the Holocene during the Little Ice Age [LIA] and has since recovered slightly to the end of the record in 2006 [at left side of graph]

Note: Another new paper claims dust from distant deserts can increase atmospheric heating by a factor of four times.

Highlights

We described biogeochemical impact of Saharan dust in lacustrine systems.

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Lacustrine evolution has been reconstructed and compared with paleo-archives.

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We speculate on meridional dust transport mechanisms.

Abstract

Saharan dust inputs affect present day ecosystems and biogeochemical cycles at a global scale. Previous Saharan dust input reconstructions have been mainly based on marine records from the African margin, nevertheless dust reaching western-central Europe is mainly transported by high-altitude atmospheric currents and requires high altitude records for its reconstruction. The organic and inorganic geochemical study of sediments from a southern Iberia alpine lacustrine record has provided an exceptional reconstruction of Saharan dust impact and regional climatic variations during the Holocene. After the last deglaciation, results indicate that Saharan dust reached Western Europe in a stepwise fashion from 7.0 to 6.0 [years before the present] and increased since then until present, promoting major geochemical changes in the lacustrine system. Effective humidity reconstruction indicates wetter conditions during the early Holocene and progressive aridification during middle–late Holocene time, boosting abrupt changes in the lacustrine system. Cyclostratigraphic analyses and transport mechanisms both point to solar irradiance and aridity as major triggering factors for dust supply over Western Europe during the Holocene.

Researchers at the University of Granada participate in an international project which has revealed that during the early phase of the Holocene (10,000 -- 6,000 years ago) the climate in the Iberian Peninsula was rather more humid than it currently is.

Scientists have found evidence of atmospheric dust from the Sahara in the depths of the Rio Seco lake, 3,020 meters above sea level, accumulated over the last 11,000 years.

A research project which counts with the participation of the University of Granada has revealed new data on the climate change that took place in the Iberian Peninsula around the mid Holocene (around 6,000 years ago), when the amount of atmospheric dust coming from the Sahara increased. The data came from a study of the sediments found in an Alpine lake in Sierra Nevada (Granada)

This study, published in the journal Chemical Geology, is based on the sedimentation of atmospheric dust from the Sahara, a very frequent phenomenon in the South of the Iberian Peninsula. This phenomenon is easily identified currently, for instance, when a thin layer of red dust can be occasionally found on vehicles.

Scientists have studied an Alpine lake in Sierra Nevada, 3020 metres above sea level, called Rio Seco lake. They collected samples from sediments 1.5 metres deep, which represent approximately the last 11,000 years (a period known as Holocene), and they found, among other paleoclimate indicators, evidence of atmospheric dust coming from the Sahara. According to one of the researchers in this study, Antonio García-Alix Daroca, from the University of Granada, "the sedimentation of this atmospheric dust over the course of the Holocene has affected the vital cycles of the lakes in Sierra Nevada, since such dust contains a variety of nutrients and / or minerals which do not abound at such heights and which are required by certain organisms which dwell there"

More atmospheric dust from the Sahara

This study has also revealed the existence of a relatively humid period during the early phase of the Holocene (10,000 -- 6,000 years approximately). This period witnessed the onset of an aridification tendency which has lasted until our days, and it has coincided with an increase in the fall of atmospheric dust in the South of the Ibeian Peninsula, as a result of African dust storms.

"We have also detected certain climate cycles ultimately related to solar causes or the North Atlantic Oscillacion (NAO)," according to García-Alix. "Since we do not have direct indicators of these climate and environmental changes, such as humidity and temperature data, in order to conduct this research we have resorted to indirect indicators, such as fossil polen, carbons and organic and inorganic geochemistry within the sediments."

This research has been conducted as part of several projects which count with the participation of scientists at the University of Granada, the Andalusian Institute of Earth Sciences (CSIC-UGR), the University of Murcia, the University of Glasgow, and the University of Northern Arizona.